1. Field of the Invention
The invention relates to a method for operating a hybrid drive train of a hybrid vehicle.
2. Description of the Related Art
The drive train of a hybrid vehicle has an internal combustion engine, a first electric machine, a transmission with an input shaft, a separating element and a first axle of the hybrid vehicle.
The internal combustion engine is arranged together with the first electric machine on the input shaft of the transmission to drive the first axle of the hybrid vehicle. Furthermore, the internal combustion engine can be connected to the first electric machine via the separating element.
The internal combustion engine can be shut down when this separating element is opened. The first axle of the hybrid vehicle then can be driven purely electrically by the first electric machine, which is operated as a motor, or can be braked by the first electric machine, which is operated as a generator (referred to below as “regeneration”) or can roll in an unpowered fashion (referred to below as “coasting”).
At high speeds, and particularly in high-power hybrid vehicles, large differences in rotational speed occur between the shut-down, that is to say stationary, internal combustion engine and the rotating first electric machine. However, if a maximum permissible difference in rotational speed is exceeded at the opened separating element, thermodynamic problems or rigidity problems can occur at the separating element.
U.S. Pat. No. 6,932,738 B2 describes a hybrid vehicle with an electric machine that can be decoupled gradually when an axle of the hybrid vehicle is driven purely electrically.
The object of the present invention is to provide a method for operating a hybrid drive train of a hybrid vehicle while avoiding thermal problems or rigidity problems at the opened separating element at high speeds of the hybrid vehicle.